Engines are usually designed with the ability to deliver a peak output, although most engine operation is performed well below this peak value. As such, it can be beneficial to operate with some cylinders inducting air without fuel injection as described in U.S. Pat. No. 6,568,177.
Engines are also designed to purge fuel vapors generated in the fuel delivery system through combustion in the cylinders. The approach for such operation described in U.S. Pat. No. 6,568,177 advantageously disables the partial cylinder operating mode when such fuel vapor purging is requested.
The inventors herein have recognized, however, that when using such an approach, there can be conditions where such frequent fuel vapor purging is necessary that the gains realized by cylinder cut-out operation are squandered. As such, less fuel economy improvement is realized than the theoretical potential. This apparent paradox can be solved by a vapor recovery control system for a vehicle having an engine with a first set of cylinders and a second set of cylinders, said system comprising:
a vapor recovery system coupled to a fuel storage system of the vehicle;
a first control valve positioned between said vapor recovery system and the first set of cylinders;
a second control valve positioned between said vapor recovery system and the second set of cylinders; and a controller for actuating said first control valve in response to a purge signal, operating said first set of cylinders to combust inducted air and purge vapor from said first control valve in said first set of cylinders at a first air-fuel ratio, and operating said second set of cylinders to operate at a second air-fuel different from said first air-fuel ratio.
By providing separate control of fuel vapors to different sets of cylinders, operation at different air-fuel ratios (such as, for example, partial fuel cut operation) can be prolonged since fuel vapor purging operation can be carried out. In this way, the full potential of disparate air-fuel ratio operation, including cylinder cut operation, can be achieved in a practical system that can accommodate significant fuel vapor purging operation. Further, for cylinder cut operation, the cylinder group in which fuel is stopped can be alternated based on operating conditions to provide more even component wear.
Note that a set of cylinders can include a number of cylinders, such as the cylinder of a bank of the engine. However, the set can include only a single cylinder, as well as some cylinders from a first bank of the engine and some cylinders from a second bank of the engine.